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I recently tried Elder Dragon Highlander/Commander, and found it to be a ton of fun. I've started customizing one of the pre-cons I got, but I'm a little confused by some of the deck-building requirements.

According to the deck-building rules:

(3) - A card's color identity is its color plus the color of any mana symbols in the card's rules text. A card's color identity is established before the game begins, and cannot be changed by game effects.

Cards in a deck may not have any colors in their identity which are not shared with the commander of the deck. (The identity of each card in the deck must be a subset of the General's)

and

(4) - A deck may not generate mana outside its colors. If an effect would generate mana of an illegal color, it generates colorless mana instead.

My question is: can I add a card to my deck that has the phrase "Add one mana of any color to your mana pool" (such as Mox Opal or Ancient Ziggurat)? Even though those cards could conceivably add black mana to my mana pool, they don't have a black or white (or any for that matter) mana symbol in their rules text, so they would be valid for inclusion in any deck? And if I had Animar as my general, I couldn't actually add {B} or {W} to my mana pool (because of rule #4), but instead I could add colorless mana?

In addition to the discussion of 'any color' below, I thought I'd point out that color identity only means mana symbols and not necessarily land names - so for instance, Verdant Catacombs is legal for your Animar deck because it doesn't provide black mana, it just has the phrase 'search for a swamp card'...
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Steven StadnickiFeb 17 '13 at 17:14

3 Answers
3

The text file found on the page you linked to with Commander info has a better description of the rules that clears this up. The important parts:

A card can't be included in your deck if any mana symbol in its mana
cost or rules text is a color not in your commander's color identity.
A card also can't be included in your deck if it has a
characteristic-defining ability defining it to be a color not in your
commander's color identity.

The cards don't have mana symbols, so you are good on that front.

During the game, if mana would be added to your mana pool that isn't a color in your commander's color identity, that much colorless mana is added to your mana pool instead.

So if you decided to add black mana to your pool via the Mox Opal, it would just add colorless.

First, you can only play cards within your commander's color identity. Second, you can only produce mana in said color identity.

Mox Opal would be legal in any Commander deck, because it is colorless and "any color" is not a color identity. However, a mana rock like Obelisk of Esper, while colorless, specifically produces W, U, or B, so it would only be legal in decks whose commander has all three of those colors in it's casting cost.

It's noteworthy that the new Extort cards don't need commanders with both Orzhov colors; most you can consider only white, or only black. This is because the W/B mana symbol for the Extort cost is in the reminder text, not the rules text.

Since your question asks about "any" EDH deck, it's worth adding an answer about the case of a colourless identity general (since other questions have expressed uncertainty about the applicability of Charles' answer).

Clearly a Mox Opal would be a legitimate card for all the reasons already stated. Other cards with similar wording/attributes follow logically. When it generates a coloured mana then, as in the coloured general case, the only relevant rule is

903.9. If mana would be added to a player’s mana pool of a color that isn’t in the color identity of that player’s commander, that amount of colorless mana is added to that player’s mana pool instead.

By 903.9 the coloured mana becomes colourless (the only available option with your general).